1. Field of the Invention
In interconnecting two pipes made of synthetic resinous material, it has been well known to insert the end part of one pipe into the connecting socket part of the other pipe end which has been provided with a relatively large diameter groove in the socket part, and to bond the two pipes by the use of some appropriate adhesives and/or a packing of a kind. Further, in connecting the pipes with the help of a packing, it was also a matter of common knowledge to form the pipes with a small clearance therebetween for the purpose of absorbing a bending external force. The pipe connecting socket part shown in FIG. 1, a partially cutaway view, for example, was constructed by thrusting a heat-softened end of a connecting pipe 1 into the core metallic mold for the purpose of molding the connecting socket part, or otherwise by inserting the latter into the former. Thus the connecting socket part 3 is provided on the inner peripheral surface of its own opening side with an annular groove 4 wherein a resilient packing 5 is to be inserted. This groove 4 was molded by a shunting metallic mold as an undercutting piece of the core metallic mold. The connecting socket part 3 thus formed had almost the same diameter, or a little larger, as compared with the spigot pipe hitherto, so it could not absorb quite a medium of variable external force.
2. Description of the Prior Art
Referring to the formation of such a type of a connecting socket part on a pipe end, the most popular is a metallic core mold as disclosed in German Pat. No. 2,242,923, such as shown in FIG. 3. This metallic core mold for forming purposes has a movable section consisting of a shifting annulus 9 slidably provided on a fixed core axle 7, another annulus 10 floatingly inserted into the shifting annulus 9, and segments 11 freely supported by the annulus 10. On the other hand, its immovable section is constituted by other segments 12 which are pivoted by a fixed annulus 13 tightly secured on the core axle 7. These segments 11 and 12 are held while impinging on both ends of a fixed sleeve 15 and shifting sleeve 14. Segments 11 and 12 are alternately disposed in a circle with the object of creating groove 4 on a connecting socket part 3 of a pipe. The figure referred to shows the segments 11 and 12 thrusted outwardly. It is with the help of a thrust spring ring provided on the shifting annulus 9 that segments 11 and 12 have been radially expanded. On rare occasion, a softened pipe 18 is press-inserted thereinto, with these segments 11 and 12 being expanded, but in ordinary circumstances, it is typical to insert the softened pipe 18 with segments 11 and 12 shunted back in the unexpanded state, and then these segments 11 and 12 are radially expanded so as to form the groove 19. The reference numeral 17 designating an outer frame which is situated directly opposite the segments 11 and 12 and forms the groove in a pipe in cooperation with the segments 11 and 12. On completing the formation, a shifting annulus 9 moves in the leftward direction by means of a working lever 8, and the thrust spring-ring of the shifting annulus 9 shunts down segments 11 and 12 to the unexpanded state from the outer circumference of the metallic core mold. At the same time, the thrust spring-ring hitches the under projections of segments 11 through the movement of the shifting annulus 9 to draw back the annulus 10. Both segments are at this point released from each other. The shifting sleeve 14 thrusts, as if embracing these segments, to the side of the fixed sleeve 15, thus helping the smooth insertion of the softened pipe 18.
For all that, it is hard to form a somewhat deep groove, particularly such as requires a sharp rising angle, by the use of such a king of pivot-supporting means of segments. This is the very reason why, owing to the short distance between the pivot-supporting part of the segments, particularly of segments on the shifting side, and the convex part which is to form the groove, the circular arc diameter generated by the convex part is small, therefore making the movement of segments 11 and 12 difficult when the depth of the undercut is great, and the much-desired groove is sometimes thereby deformed. Accordingly, the metallic core mold of this type is unsatisfactory for the formation of a deep groove. In addition, it can be applied only to short-sized segments. As a natural consequence, there is no choice but to consider another new means for the simultaneous forming of a desired number of grooves using segments having a relatively long forming surface wherewith a groove for elastic packing and a space in the connecting socket are formed. In other words, in a metallic core mold which is composed of segments having long forming surfaces, the circumferential forming surface of the segment group must be able to shift and displace, maintaining continually nearly a parallel state to the axis of the metallic core mold, at the time of their assembling and dismantling.